This invention relates to air blast fuel injectors of the type in which fuel is atomised by a fast flowing stream of air to produce a fuel-air spray.
A known air blast fuel injector comprises a concentric arrangement of air and fuel injection ports through which air and fuel are injected so that a swirling cone of air meets a conical film of fuel and produces an annular spray. A simplex type of injector has a single fuel supply. A duplex type of injector has pilot and main fuel supplies, each of which is atomised by a corresponding swirl of air. For example, a known duplex air blast fuel injector comprises a concentric arrangement of an inner air swirler, a pilot fuel filmer, an intermediate air swirler, a main fuel filmer and an outer air swirler. This arrangement claims to produce a pilot spray in an inner recirculation or combustion zone and a main fuel spray in an outer recirculation or combustion zone, but performance and stability tests indicate that the main fuel spray is not independent of the pilot fuel spray. The position of the pilot zone internally of the main zone may make it difficult to ignite reliably.
It is an object of the invention is to provide a alternative duplex air blast fuel injector.
According to one aspect of the present invention there is provided an air blast fuel injector comprising inner and outer fuel injection ports, first and second air swirlers associated with said inner and outer fuel injection ports to direct air and fuel sprays into inner and outer recirculation zones, the outer zone being arranged to be a pilot combustion zone and the inner zone being arranged to be a main combustion zone.
Preferably, the first air swirler is located inside the inner fuel injection port, the second air swirler is located inside the outer fuel injection port and the injector includes an intermediate air filmer located between the inner fuel injection port and the second air swirler arranged to produce an intermediate curtain of air separating the air and fuel mixtures in the two zones.
According to a second aspect of the present invention there is provided an air blast fuel injector comprising inner and outer fuel injection ports, first and second air swirlers associated with the inner and outer fuel injection ports to direct air and fuel sprays into inner and outer recirculation zones, and an intermediate air filmer between the inner and outer fuel injection ports arranged to produce an intermediate curtain of air separating the air and fuel mixtures in the two zones.
The intermediate air filmer is preferably located between the inner fuel injection port and the second air swirler. The intermediate air filmer is preferably an axial air filmer. The intermediate air filmer may be arranged to produce a low swirl compared with that of the inner air swirler. The fuel injector may include an outer air swirler located outside the outer fuel injector. The inner fuel spray is preferably arranged to have an angle of substantially 90xc2x0 and the outer fuel spray is preferably arranged to have an angle of substantially 140xc2x0.
The invention will now be described by way of example with reference to the accompanying drawings.